Load patches serve to provide attachment points for securing various components including moorings, handling lines, and propulsion systems to the hulls of pressurized airships. Pressurized airships use a fabric skin for their hulls, which is expandable to accommodate changes in atmospheric pressure and temperature. Conventionally, the load patches are adhesively bonded directly to the fabric skin.
Generally, load patches are used to distribute the concentrated loads from the attachment of the moorings, handling lines, and propulsion systems into the fabric skin. Typically, conventional load patches are configured to disperse the concentrated loads radially outward away from the point of attachment of the respective component. To that end, conventional load patches usually have triangular shapes.
However, use of a conventional load patch leads to the development of relatively large strains concentrated along the fabric skin. For example, when attaching a conventional load patch to the fabric skin, the entire surface of one side of the load patch is adhesively bonded to the fabric skin to define a lamination area. During inflation of the pressurized airship, and changes in atmospheric pressure, the lamination area generates resistance to expansion within the fabric skin, and such resistance causes relatively large strains to develop along the fabric skin.
Due to the formation of the lamination area, relatively large strains develop during expansion of the fabric skin. These relatively large strains can be concentrated in areas of the fabric skin surrounding the lamination area. The effects of relatively large strains concentrated around the lamination area can be exacerbated when using the conventional load patches on a pressurized airship configured for high-altitude operation. There is a concern that the development of relatively large strains around the lamination area could cause a tear in the fabric skin resulting in catastrophic failure of the airship.
To illustrate the development of relatively large strains concentrated around the lamination area, FIGS. 1A, 1B, 1C, and 1D are provided. FIGS. 1B-1D are color representations of strains applied to a prior art load patch. Although not absolutely required for understanding the product, it is believed that FIGS. 1B-1D aid in understanding the prior art. And although dimensions are provided in the drawings, they are for reference only and should not be construed as a limitation.
FIG. 1A depicts a conventional load patch 10 bonded to a fabric skin 12 forming the hull of a pressurized airship. Together, the conventional load patch 10 and fabric skin 12 define a lamination area designated generally by the numeral 13. The conventional load patch 10 is triangularly shaped with a rear edge 14, a first angled edge 16 and a second angled edge 17. The first angled edge 16 and second angled edge 17 intersect at an apex 18. A load of 2000 lbf. load is applied to the conventional load patch 10 at the apex 18. The applied load simulates the concentrated loads applied by the moorings, handling lines, propulsion systems or other component secured to the fabric skin 12 through the conventional load patch 10.
The fabric skin 12 is constructed from a material that expands significantly during inflation of the pressurized airship, and changes in atmospheric pressure and temperature. FIG. 1A and the background of FIGS. 1B, 1C, and 1D demonstrate the deformation of the fabric skin 12 during expansion and application of different applied loads utilizing various colors to indicate the relative amounts of strain sustained by the fabric skin 12. A color gradient is used to represent the relative amounts of strain, which may range from red, indicating high amounts of strain, to purple/blue, indicating low amounts of strain.
In addition, FIGS. 1B, 1C, and 1D were developed using a SHELL finite element model employing classical laminate theory to depict the resistance to expansion that is generated by the lamination area 13, and to illustrate the strain generated as various colors related to percentages of maximum allowable strain. For example, FIGS. 1B, 1C, and 1D depict the strain developed in various areas along the fabric skin 12 as percentages from 0-68% of the maximum allowable strain in those areas. The gradations in color, as previously mentioned, indicate which of the various localities along the fabric skin 12 are experiencing the largest relative amounts of strain.
Because of the resistance to expansion generated by the lamination area 13 along the fabric skin 12, and due to the application of the applied load, differing amounts of strain develop along the fabric skin 12 due to expansion. FIGS. 1B, 1C, and 1D are provided to illustrate the differing amounts of strain developed along the fabric skin 12 in three (3) directions due to the resistance to expansion and the applied load. FIG. 1B depicts the amount of strain developed in the axial direction, FIG. 1C depicts the relative amount of strain developed in the transverse direction, and FIG. 1D depicts the relative amount of strain developed in the negative bias direction (oriented at forty-five degrees (−45°) with respect to the axial direction and transverse direction). It should be appreciated that a high amount of relative stress is sustained by the conventional load patch 10 is found in each of the axial, transverse, and negative bias directions, as indicated by the various red areas shown in FIGS. 1B-D.
As seen in FIG. 1B, relatively large strains, indicated as red areas, are found in the axial direction that projects outwardly from the rear edge 14, and in areas along the first angled edge 16 and second angled edge 17 adjacent the apex 18. Furthermore, as seen in FIG. 1C, relatively large strains in the transverse direction are concentrated in large areas projecting outwardly from the first angled edge 16 and second angled edge 17 near the rear edge 14. And, as seen in FIG. 1D, relatively large strains in the negative bias direction are concentrated in large areas projecting outwardly from the first angled edge 16, and from the rear edge 14 near its intersection with the second angled edge 17.
As illustrated in FIG. 1C, relatively large strains are developed around the lamination area 13 in the transverse direction. Because the application of the applied load is in the axial direction, and, hence, in a direction perpendicular to the transverse direction, the applied load has limited responsibility for the relatively large strains developed in FIG. 1C. The relatively large strains depicted in FIG. 1C are developed due to resistance to expansion generated by the lamination area.
When relatively large strains are concentrated in particular areas along the fabric skin 12, those areas are susceptible to catastrophic failure, and can result in tearing of the fabric skin 12. Because the relative amounts of strain depicted in FIGS. 1B, 1C, and 1D are shown in proportion to sixty-eight percent (68%) of the allowable strain in those areas, the relatively large strains concentrated in the areas 26, 27, and 28 are within the allowable strain limits established for those areas. However, if the fabric skin 12 undergoes greater expansion, the relatively large strains concentrated around the conventional load patch 10 will be exacerbated, and will likely cause the fabric skin 12 to tear.
Therefore, while use of conventional load patches is suitable for pressurized airships configured for low altitude operation, such conventional load patches are unsuitable for high-altitude pressurized airships. Such high-altitude pressurized airships require their fabric skin to expand significantly. As discussed above, the conventional load patches would likely cause the fabric skin of high-altitude pressurized airships to tear because of the strain concentrations developed around the lamination area. Due to significant expansion of the fabric skin, high-altitude pressurized airships require use of load patches which limit development of strain concentrations along the fabric skin. Such load patches should limit contact with the fabric skin of the high-altitude pressurized airships, and be composed of materials which efficiently distribute the applied load to the fabric skin.